1. Field of the Invention
The invention relates to a connection bracket, which is provided in order to connect a connection means to a flange, which in particular is the flange of a tower element for a wind turbine. Typically, shackles, hooks, rings or the like, by means of which a carrying means such as for example a cable, strip or belt can be detachably coupled with the connection bracket, serve as connection means to be coupled with the connection bracket.
2. Description of Related Art
The steel towers, carrying the hub of a rotor, of modern wind turbines are normally composed of a plurality of pre-fabricated, hollow-cylindrical tower elements. Normally, flanges directed inwardly are formed on the foot and head ends of these tower elements. Through-openings are moulded into the flanges at regular distances, which through-openings are aligned in the assembled state to the through-openings of the associated flange of the respective next highest or next lowest arranged tower element. Bolts are then inserted through the through-openings in order to connect the tower elements to one another.
Today, wind turbines are built with hub heights of over 100 m, such that the tubular tower elements with a wall thickness of 20 mm to 40 mm easily reach a mass in the high double-digit tonne range.
The diameter of the pre-fabricated tower elements is generally considerably smaller than the length thereof. Therefore, the tower elements are transported horizontally to the site of the wind turbine to be erected. At the site of the wind turbine they therefore not only need to be lifted by means of a suitable crane from the heavy goods transporter or ship used for conveying it and swivelling it into its final position, but they also need to be rotated from the horizontal alignment into a vertical alignment in order to set them down on a foundation or a tower element that has already been erected.
In order to make this possible using conventional lifting means, normally connection brackets of the type in question here are fixed to the flanges of the tower elements. As a rule, the through-openings present in the flanges are used for this.
High demands are placed on the connection brackets with regard to their load capacity and performance characteristics. Thus, they not only need to have a sufficient carrying capacity and be able to withstand the tough operating conditions, but they also need to make it possible for the tower elements to be aligned with pinpoint accuracy by means of the simple aids available at the site. At the same time, they need to be set up in such a way that the danger of injury to personnel on the site is minimised.
For lifting and aligning the tower elements, typically four connection elements are required on the head flange present at the upper end of the tower element and two connection elements on the foot flange present at the lower end of the tower element. The four connection elements associated with the head flange are distributed at regular angular distances over the periphery of the head flange and are screwed in place there such that the two upper connection elements and the two lower connection elements are respectively located substantially at a height in the tower element while it is still lying down.
The two connection elements associated with the foot flange are screwed on in the tower element that is lying down respectively above the centre line thereof at a distance from each other that is sufficiently large to keep the tower element in a stable position in relation to its longitudinal axis while it is lifted from the respective transporter and erected.
To erect a tower element, a first end of a supporting cable is attached onto the two connection elements, in the upper position on said tower element when it is lying down, of the head flange, for example by means of one shackle each. Each of these cables is then guided over a cable pulley, which hangs on the hook of a first crane, and, with its other end, is in turn coupled by means of a suitable connection means onto the lower connection element located respectively under the associated upper connection element.
In a comparable way, the two connection elements of the foot flange are connected to the hook of a second crane by means of a cable.
To erect the tower element, the latter is firstly lifted evenly by both cranes while maintaining its horizontal alignment, until a sufficient ground clearance is achieved. Then, the end of the tower element associated with the head flange is lifted to a greater extent such that the tower element in steadily converted into a vertical alignment. In this process, the cable pulleys guarantee that at all times the forces are introduced evenly into the cable strands in all four connection elements screwed onto the head flange, while the two connection elements attached to the foot flange serve as counter-bearings.
As soon as the tower element is aligned vertically, the carrying means associated with the foot flange are relieved of their load and the corresponding connection elements can be disassembled. In this state, the tower element now hangs only from the four connection elements screwed onto the head flange. Once the connection elements have been removed from the foot flange, the tower element can be swivelled into the intended end position and screwed in place there onto the foundation or the tower element already present.
During the erection process, the respective carrying means used (cable, strip) are subjected to considerable loads. They must therefore not only absorb the load of the tower element, but at the same time they are also moved relative to the cable pulleys of the cranes. In particular in the carrying means associated with the foot flange of the tower element to be erected, there is also the danger that during the erection the carrying means is pulled over one of the comparatively sharp-edged outer edges of the tower. Due to the relative movements that unavoidably occur there during erection, this leads to considerable wear through rubbing in the affected region of the carrying means. This can very quickly go so far that the carrying means becomes unusable. For this reason, the clear stipulation exists that the connection elements used for attaching the carrying means to the flange must guide the respective carrying means such that rubbing against an outer edge of the tower element is excluded.
This requirement can be fulfilled using a known “flange load-ring”. The known flange load-rings are composed of a plate-shaped fixing section, which is provided with openings for screwing-in on a flange of the respective tower, and a ring element pivotably mounted on the fixing section.
In the known flange ring, two bolts aligned coaxially to each other are tangentially welded onto the ring element and sit in corresponding bearing openings of the fixing section and thus define the swivel axis of the ring element. The bearing openings are arranged on a longitudinal side of the fixing section in relation to the fixing openings thereof such that the swivel axis in the flange load-ring assembled on the respective flange of a tower element is arranged outside the periphery of the tower element. In this way, it is guaranteed that the carrying means is guided during swivelling of the tower element such that it does not come into contact with any edge of the tower element.
However, the known flange load-rings are expensive to manufacture due to their elaborate design. In addition, they need to be constructed with sufficient weight that they can absorb the loads to which they are subjected in practical use with the necessary security. This leads to such a great weight that they are difficult to handle on site.
Against this background, the object of the invention was to make available a connection element that can be manufactured cost-effectively, in which a high safety of use is guaranteed despite a reduced weight.